Modal
verbs are used to talk about ability, possibility, obligation, prohibition, or to make requests or offers. 情态动词用于谈论能力、可能性、义务、禁止，或提出请求或提议。
Can
能力 Ability: I can play the piano very well.
许可 Permission: Can I go now?
可能性 Possibility: It can be a very good day tomorrow.
提议 Offer: I can help you with this homework. Don't worry!
请求 Request: Can you please pass me the salt?
Could
过去的能力 Ability in the past: I could play the piano well when I was 9.
礼貌的允许 Polite permission: Excuse me, could I come in?
可能性 Possibility: A hailstorm could come here tomorrow.
礼貌的提议 Polite offer: No problem. I could give you a lift.
礼貌请求 Polite request: Could you please move to the next slide?
May
许可 Permission: May I leave early?
可能性 Possibility: Astronauts may discover life in other planets.
Might
礼貌的允许 Polite permission: Might I take you home?
可能性 Possibility: I might visit him tomorrow if the weather is nice.
Must
义务 Obligation: You must do homework.
确定性 Certainty: He must be at the cinema now. He told me about that yesterday.
Mustn't
禁止 Prohibition: You mustn't play here. It's dangerous.
Will
预测 Prediction: The weather forecast predicts that it'll rain tonight.
承诺 Promise: I'll finish all the homework by Friday.
自发的决定 Spontaneous decision: I'll lend you some money.
请求或要求 Request / demand: Will you please give me that book?
Would
用作“will”的过去形式 Used as the past form of “will”: My dad said that he would give me some toys on my birthday.
礼貌的请求/要求 Polite request / demand: Would you mind closing the door, please?
Shall
预测 Prediction: This time tomorrow I shall be in London.
提议或建议 Offer/ suggestion: Shall we discuss this further with him?
Should
建议 Advice: You should see the doctor. It's swollen.
预测或期望 Prediction/ expectation: The project should be done before May.
礼貌的建议 Polite suggestion: Should I call her to say sorry?
Ought to
义务 Obligation: You ought to say good bye to your parents when you leave.
建议 Advice: You ought to sleep early. You look really tired.
Needn't
用来谈论不必要的事情 Used to talk about something not necessary:
You needn't give him any advice. He won't listen.
